Electrical discharge device



Aug- 23. 1966 J. D. WOERMBKE 3,263,757

ELECTRICAL DISCHARGE DEVICE Filed July 7, 1961 F ig. I.

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WITNESSES INVENTOR W @M, James D. Woermbke.

AT'TORNEY United States Patent 3,268,757 ELECTRICAL DISCHARGE DEVICEJarnes D. Woermbke, Linthicum, Md., assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of Pennsylvania FiledJuly 7, 1961, Ser. No. 122,456 6 Claims. (Cl. 313--223) This inventionrelates, in general, to gas filled electrical discharge devices and moreparticularly to atmospheres for filling transmit-receive switches,hereafter referred to as T-R switches, used in conjunction with radarequipment.

T-R switches have been widely used in radar circuits to permit asensitive receiver of ultra short-wave signals, for example, 3000megacycles, to be operatively connected to the same antenna of a radarset to which the transmitter is connected. The T-R switch functions toshort circuit the receiver the moment a pulse from the transmitter istransmitted to the common antenna and thus prevents an influx of powerinto the receiver, from the transmitter, which would damage thesensitive receiver.

To effect the above purpose, the T-R switch must change with greatrapidity from a nearly non'conductive state to a sufficiently conductivestate when the pulse wave front appears, and must change back again tothe nonconductive condition with great rapidity when the trans mittedpulse has terminated. To effect this change, it is necessary that thegas within the switch shall rapidly increase in ionization so that aspace discharge may be initiated by a relatively small voltage rise,i.e., it should have a comparatively low breakdown voltage, and itshould deionize rapidly when the voltage is removed so that the returnsignal may be admitted to the receiver.

One form of T-R switch comprises a chamber which contains a quantity ofionizable gas such as argon. A resonant microwave aperture or iris islocated in one wall of the chamber. With the incidence of high powerlevel electromagnetic waves, a very high voltage occurs between oppositeedges of the iris causing ionization of the gas within the chamber. Thisionized gas forms a low resistance path between the opposite edges ofthe iris through which an arc discharge is established and which, inturn, effectively short circuits the path across the iris causing thereflection of incident radiation.

It has been suggested, in the prior art, that a small quantity of anelectron attachment gas, such as iodine, be admixed with the ionizablegas contained in the chamber of the TR switch for the purpose of rapidlyattracting electrons from the ionized gas and hence deionize the gas atthe termination of the transmitted pulse. Iodine has a low vaporpressure at room temperature but is heated within the switch by are losseffects, so that its vapor pressure is increased to usable levels if theswitch is operated at a sufiiciently high incident power level.Frequently, however, microwave T-R switches are required to operate overa broad range of incident power levels, the lower limits of which arenot sufficiently high to heat the iodine to a usable level.

Accordingly, it is the general object of this invention to provide a newand improved TR switch which is effectively operable over a wide rangeof incident radio frequency power levels.

It is another object of this invention to provide a gaseous atmospherefor electron discharge devices.

It is a more particular object of this invention to provide a gaseousatmosphere for electron discharge devices, which atmosphere will ionizeand deionize with great rapidity over a wide range of incident powerlevels.

Briefly, this invention accomplishes the above cited objects byproviding a T-R switch having an enclosed atmosphere comprising aplurality of types of attaching gases or agents. The attaching gases areselected so that each acts as the dominating attaching agent atdifferent levels of incident radio frequency power so that the T-Rswitch will effectively operate over a much wider range of incidentradio frequency power than TR switches of the prior art.

The aforementioned and other objects are effected by this invention aswill be apparent from the following description read in conjunction withthe accompanying drawing, in which:

FIGURE 1 is a schematic showing the basic components of a radar systememploying a T-R switch;

FIG. 2 is a side elevation view, in section, of a T-R switch inaccordance with the invention; and

FIG. 3 is an elevational front view showing one form of iris which maybe utilized with the invention.

Referring particularly to FIG. 1, there are shown the basic componentsof a radar transmitter-receiver system. This includes a transmitter 10which generates pulses of short duration which are transmitted through awaveguide 12 to a radiating antenna (not shown). Returning signals areintercepted by the same antenna and returned through waveguides 12 and14 to a receiver 16.

In order that the receiver 16 may not be damaged by the transmittedsignal, which is of much higher power level than the received signal, itis necessary that means he provided to effectively block the transmittedsignal from the receiver during the transmitting period. This isaccomplished by interposing in the waveguide 14 an electronic switchingdevice indicated generally at 7, ordinarily referred to as a T-R switch.This switch comprises generally a sealed enclosure 15 having microwaveirises 22 and 24 through which radio frequency wave energy may pass andcontains an ionizable gas adapted to support a discharge. With theincidence of high power electromagnetic waves, a discharge isestablished within the enclosure which effectively short circuits thewaveguide 14 and prevents the transmitter energy from entering thereceiver.

In order that the returning signal, which is at a much lower power levelthan the transmitted signal, may not also be blocked from the receiver,it is, of course, imperative that the TR switch return to anon-conductive state within a matter of microseconds after thetermination of the transmitting pulse. The rate at which the T-R switchwill return to the non-conducting state is governed largely by the rateat which the gas within the envelope returns to the deionized stateafter the transmitter voltage has been removed. The rate at which thisdeionization will occur is largely governed by the nature of the gaseousatmosphere within the envelope.

In FIGS. 2 and 3 there is shown in greater detail, a T-R switch similarin function to that described in connection with FIG. 1. The switchcomprises a sealed envelope 26 which is made of some suitable materialsuch as glass or quartz and is filled with a gaseous atmosphere as willbe explained later.

A metallic diaphragm 28 having an aperture or iris indicated generallyat 29 is bonded by suitable means such as soldering or brazing to anexternal wall of the envelope 26. The iris 29 is of such shape anddimensions so as to be resonant at the operating frequency of the radarsystem. By way of example, as shown in FIG. 3, the iris is in the formof two separated circular openings 30, 30, connected by a slot 32symmetrical to a line extending between the centers of the openings 30,30. The circumferences of the openings constitute inductive portions andthe margins of the slot 32 constitute capacitive portions of the iris.The iris acts to concentrate the incident radio frequency field at itsconstricted portion to define a discharge gap within the envelope 26 andto reduce the power level necessary to initiate the discharge. Thisconcentration also aids in the reduction of arc loss after discharge hasbeen established.

The envelope 26 is hermetically sealed and contains a gaseousatmosphere. This gaseous atmosphere comprises, in part, an ionizablebody gas to facilitate discharge within the envelope 26 upon theincidence of radio frequency power from the transmitter. The ionizablebody gas may consist of any of the noble gases, that is helium, neon,argon, krypton, xenon or radon. These gases are readily ionizable andserve to provide, in their ionized state, a low resistance dischargepath. While these gases will ionize in a sufficiently short time and ata low incident voltage to effect the proper switching of the tube, theircutoff time, that is the time in which it takes for the gases todeionize is comparatively long and thus these gases acting alone may notcease to conduct within a sufficiently short time to permit the returnedpulse to be admitted into the receiver.

It may be, therefore, necessary to admix with these body gases someelectron attaching agent for the purpose of removing electrons from theionized atmosphere, thus increasing the speed with which the atmospherewithin the envelope 26 will deionize and hence, interrupt the aredischarge. Care, however, must be taken in the selection of the electronattaching agents for although they increase the speed at which thegaseous atmosphere deionizes, they also increase the power levelnecessary to initially ionize the body gas. In the case of T-R switchesdesigned to operate over a wide band of incident radio frequency powerinput, the problem of selection of the proper electron attaching agentis particularly acute. If too much attaching agent is used, then theinitial breakdown voltage of the switch may be too high and damage mayresult to the receiver. On the other hand, if too little attaching agentis used, then it may be insufficient at high input levels to effectivelydeionize the body gas. The latter will result in a slow recovery time.

In accordance with this invention, two distinct attaching agents areused in the atmosphere within a single T-R switch. The first of theseagents is predominant at relatively low incident radio frequency powerlevels and the second is predominate at higher power levels. A typicalexample of an atmosphere embodying the present invention comprises abody gas of argon at a partial pressure of from 4 to 6 millimeters ofmercury, a first attaching agent chlorine at a partial pressure of from0.8 to 1.5 millimeters of mercury, and a second attaching agent iodineat about 0.3 millimeter of mercury partial pressure all at C. Thechlorine acts as the predominate attachment agent at the lower powerinput levels. The iodine which has a very low vapor pressure at roomtemperature but which increases rapidly with a rise in temperature, actsas the dominating attachment agent at the higher power input levels byvirtue of its increased partial pressure. This increase in pressure iscaused by the increase of gas temperature occasioned by the greater areheating at these higher power levels. This attachment gas combinationyields the desired initial low firing level, since the ratio of chlorineplus iodine to the body gas (argon) is low, while simultaneouslyproviding for a fast recovery time at both high and low incident radiofrequency power levels.

It is recognized that the chlorine may be replaced as the low powerlevel attachment agent by gases such as bromine, carbon tetrafluoride orsulfur tetralluoride.

While a specific embodiment of the invention has been shown anddescribed in this application, it will be apparent to those skilled inthe art that various changes and modifications may be made thereinwithout departing from the essential features of the invention.

I claim:

1. A gaseous discharge device comprising an envelope, means defining adischarge gap within said envelope, and a gaseous atmosphere within saidenvelope comprising an ionizable body gas admixed with chlorine andiodine.

2. A gaseous discharge device comprising an envelope, means defining adischarge gap within said envelope, and a gaseous atmosphere within saidenvelope comprising a body gas taken from the group consisting ofhelium, neon, argon, krypton, xenon and radon admixed with iodine andanother electron attachment agent taken from the group consisting ofchlorine, bromine, carbon tetrafluoride and sulfur tetrafiuoride.

3. An envelope, means defining a discharge gap within said envelope, anda gaseous atmosphere within said envelope consisting of a body gas takenfrom the group consisting of helium, neon, argon, krypton, xenon andradon and two different electron attachment agents one taken from thegroup consisting of chlorine, bromine, carbon tetrafiuoride and sulfurtetrafiuoride and the other iodine, the two electron attachment agentsbeing such that at low incident radio frequency power levels one acts asthe dominating attachment agent and at higher incident radio frequencypower levels the other becomes the dominating attachment agent by virtueof its increased partial pressure.

4. A gaseous discharge device comprising an envelope, means defining adischarge gap within said envelope, and a gaseous atmosphere within saidenvelope comprising argon at a partial pressure of from 4 to 6 mm. ofmercury, from 0.8 to 1.5 mm. of mercury partial pressure of chlorine,and approximately 0.3 mm. of mercury partial pressure of iodine at 20 C.

5. An envelope, means defining a discharge gap within said envelope, agaseous atmosphere within said envelope comprising a body gas taken fromthe group consisting of helium, neon, argon, krypton, xenon, and radonand first electron attachment agent of iodine and second electronattachment agent taken from the group consisting of chlorine, bromine,carbon tetrafluoride and sulfur tetrafiuoride, said first electronattachment agent being predominate at higher internal envelopetemperatures and said second electron attachment agent being predominateat lower internal envelope temperatures.

6. A T-R switch comprising a resonant apertured diaphragm defining adischarge gap, an envelope atfixed to one side of said diaphragm toprovide a discharge path through said envelope and a gaseous atmospherewithin said envelope comprising argon at a partial pressure of from 4 to6 mm. of mercury, from 0.8 to 1.5 mm. of mercury partial pressure ofchlorine, and approximately 0.3 mm. of mercury partial pressure ofiodine at 20 C.

References Cited by the Examiner UNITED STATES PATENTS 2,590,108 3/1952Liebson 313-224 X 2,729,762 1/1956 Hagen et a1. 313-224 X 2,776,3901/1957 Anton 313-93 2,799,804 7/1957 Biondi 313- X 2,845,577 7/1958Smullin 313-13 X 3,019,363 1/1962 Weichering 313-224 X DAVID J. GALVIN,Primary Examiner.

GEORGE WESTBY, Examiner.

P. C. DEMEO, C. R. CAMPBELL,

Assistant Examiners.

1. A GASEOUS DISCHARGE DEVICE COMPRISING AN ENVELOPE, MEANS DEFINING ADISCHARGE GAP WITHIN SAID ENVELOPE, AND